1. Field of the Invention
Apparatuses consistent with the present invention relate to a transmissive active grating device, and more particularly, to a transmissive active grating device transmitting or diffracting a light according to an applied voltage.
2. Description of the Related Art
Active grating devices, which perform as gratings for diffracting light according to an applied voltage, are combined with optical systems in order to be used as light modulators in laser printers or display devices.
FIG. 1 is a perspective view of a conventional reflective active grating device 10. Referring to FIG. 1, the conventional reflective active grating device 10 includes a plurality of ribbon layers 14 that are suspended from a substrate 11 in parallel with each other. FIGS. 2A and 2B are cross-sectional views showing a structure and an operation of the conventional reflective active grating device 10 in more detail. Referring to FIGS. 2A and 2B, the conventional reflective active grating device 10 includes an insulating layer 12 formed on the substrate 11, an electrode layer 13 formed on the insulating layer 12, the ribbon layers 14 suspended from a top surface of the substrate 11, and reflective layers 15 formed on top surfaces of the ribbon layers 14. The reflective layers 15 can be formed of a metal material having a superior conductivity and a high reflectivity such as aluminum, and thus, can perform as both a reflective layer and an electrode layer.
In this structure, if a voltage is not applied to the electrode layer 13 and the reflective layers 15, all of the ribbon layers 14 are located at the same height as shown in FIG. 2A since the reflective layers 15 remain still. Therefore, light incident onto the conventional reflective active grating device 10 is reflected by the reflective layers 15 that are formed respectively on the ribbon layers 14. Hence, if a shutter is appropriately installed on a light path of the reflected light, a dark state occurs.
On the other hand, when a positive voltage (or a negative voltage) is applied to the electrode layer 13 and a negative voltage (or a positive voltage) is alternately applied to every second reflective layer 15, every second ribbon layer 14 moves toward the substrate 11 due to an electrostatic attraction between the reflective layers 15 corresponding to every second ribbon layer 14 and the electrode layer 13 as shown in FIG. 2B. Then, the conventional reflective active grating device 10 performs as a reflective diffraction grating as shown in FIG. 3. Therefore, the light incident onto the conventional reflective active grating device 10 is diffracted and reflected by the reflective layers 15 respectively on every second ribbon layers 14. Hence, since a shutter is installed on a light path of 0th order diffracted light, ±1st or high order diffracted light are not blocked, and thus, the light proceeds. Therefore, in this case, a bright state occurs.
However, the conventional reflective active grating device 10 is a three-dimensional structure involving a mechanical movement, and thus, conventional reflective active grating device 10 must undergo a micro-electro-mechanical system (MEMS) process which is a very delicate process. In addition, since the conventional reflective active grating device 10 involves a mechanical movement, a response speed of the conventional reflective active grating device 10 is limited to a few KHz. Moreover, since the conventional reflective active grating device 10 reflects the incident light, the light path is bent and the optical system becomes complex.